This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The objectives of this study are to compare the pharmacokinetic (PK) profiles of temozolomide (TMZ) in patients who develop severe (grade 3-4) thrombocytopenia to the PK profiles in patients who do not develop severe thrombocytopenia while receiving standard first-line therapy and to determine if patients with high-grade gliomas who develop thrombocytopenia while receiving standard first-line therapy have any single nucleotide polymorphisms in the O 6-methylguianine-DNA methyltransferase (MGMT) gene.